This dog is clearly fear aggressive- his eyes are very wide, his lips are turned down, his body position is more flight (turning away from the scary thing) than fight (staring square onto the scary thing). He's realized that he make any scary thing go away with this behavior. To make this dog behave on a leash, we have to desensitize and countercondition him to like whatever he is afraid of. It's not as hard as you think!
This dog is pulling because he's over exuberant. His face is happy, lips turned up, ears pointed forwards in anticipation, body is relaxed not tense. He needs a completely different plan for his leash reactivity than the dog on the left!
Leash reactivity can be a very scary thing for both you the owner and everyone your dog lunges at. It's pretty dangerous too, if you were to be pulled down and hurt, or not be able to hold onto your dog. Most people just give up walking their dog if it behaves this way. But one can't give up taking the dog to the vet clinic, so good leash behavior is a must-learn skill for all dogs.
There are a couple of reasons why your dog may have leash reactivity. The most common is fear aggression; dogs are more anxious about scary things like Strangers or unknown dogs when they know they are "trapped" on a leash. Another cause could be over exuberance in the possibility of meeting a new playmate- the dog could be reacting out of frustration, not aggression.
The good news is that both causes are treatable. If fear aggression is the cause, you can read about treatment here. If your dog is over-exuberant, it's even easier to help you and your dog enjoy a walk. We start with proper fitting of a harness or head collar (see our recommendations on our shopping page here). We NEVER use training devices that cause pain or discomfort such as choke or prong collars, shock collars, collars that cut under the armpits to stop pulling, etc. We want the dog to enjoy nice, calm leash walks!
Our fabulous positive trainers can help you make leash walking a joy. Contact Come, Sit, Stay in Sanford or Sandhills Dog Training in the Southern Pines areas. We have fully vetted these trainers and are confident that they use only positive training methods based on current animal behavior science for results that work.